The present invention relates in general to a method for the non-contact determination of an overfilling of a receptacle filled with a filling product, wherein an envelope curve is generated from echo signals reflected on a filling product surface. Moreover, the present invention relates to an evaluation arrangement for realizing a method of this kind, and a filling level measuring device equipped with an evaluation arrangement of this kind.
Filling level measuring devices of the kind of interest here, work in particular according to the so-called pulse echo principle and scan a reflected echo signal.
Filling level measuring devices working on the pulse echo principle and scanning a reflected echo signal, generate from the scanned echo signal a series of data as to each echo in the echo image or the so-called envelope curve. Generating an envelope curve from echo signals is sufficiently known and, accordingly, further explanations as to this technology are not required here (cf., for example, German Patent DE 44 07 369 C2; M. Scholnik xe2x80x9cIntroduction to Radar Systemsxe2x80x9d, 2nd edition, 1980, McGraw-Hill; Peter Devine xe2x80x9cRadar level measurementxe2x80x94the user""s guidexe2x80x9d, VEGA Controls Ltd., 2000, ISBN 0-9538920-0-X).
Conventional filling level measuring devices are capable of detecting the filling level by measuring individual echoes in the envelope curve. Thus, the envelope curve is, for example, examined with low-pass filters, in particular a pull-down low-pass filter. In this way, the echoes are searched in ranges, which have been previously fixed by the intersection point of a detection threshold and the echo signal. Thus, an echo in the envelope curve is characterized by various features, such as, for example, amplitude, echo width at a certain amplitude below the peak, and the ascending gradient of the scanned echo signal before the peak. In this manner, the actual useful echo is ascertained, i.e. the echo, which has been reflected by the actual filling product surface, in particular separate from the other echoes and the dying-out transmission signal.
With this kind of signal processing, the problem arises in the short range of the sensor, that echoes interfere with the transmission signal which has not yet died out. With filling level sensors according to prior art accordingly, there can no longer be ascertained an unequivocal statement as to the filling level with an overfilling of a receptacle to be monitored. This can even lead to false measurements under certain circumstances. As soon as this condition arises, it can be recognized as an overfilling, what hitherto caused problems.
European Patent Application EP 0 871 019 A1 describes a method for the determination of an overfilling during the measurement of a filling level by means of an ultrasonic transducer. In this method, an overfilling is ascertained when the ultrasonic transducer is immersed in the filling product, here a liquid, or is covered by it. For determining the overfilling, the dying-out output signal of the ultrasonic transducer generated by the post-pulse oscillation of the ultrasonic transducer at the end of each ultrasonic transmission pulse, is evaluated. Thereby, it is taken advantage of the fact that the duration of the post-pulse oscillation is shorter due to the better coupling of the ultrasonic transducer to the liquid than to air, when the ultrasonic transducer is covered by the liquid. This method is technically realized in that the duration of the post-pulse oscillation of the ultrasonic transducer, until the drop to a predetermined amplitude value, is compared to a predefined time limit value. As an alternative, the amplitude of the post-pulse oscillation of the output signal of the ultrasonic transducer is compared in a predetermined moment after the end of the alternating voltage pulse, to a predefined threshold value, which is rated so that it is fallen below when the ultrasonic transducer is covered by the liquid. A further alternative consists in that the amplitude of the post-pulse oscillation of the output signal of the ultrasonic transducer is integrated in a determined time window after the end of the alternating voltage pulse, and the integration value is compared to a predefined threshold value, which is rated so that it is fallen below, when the ultrasonic transducer is covered by liquid.
In summary, it has to be stated that all of the methods disclosed in this publication have in common that a determined threshold value or time limit value has to be fallen below so as to identify an overfilling. All methods are in particular based on the technical effect that, when it is immersed in a liquid, an ultrasonic transducer dies out in a considerably faster manner than when it oscillates in air. Exactly this effect is now referred to for determining an overfilling. What happens to the emitted echoes, remains unobserved. Therewith, this kind of determining an overfilling can only be applied with ultrasonic transducers, and it is, moreover, only reliable, when an overfilling may be equaled to an coverage by or immersion in a liquid. Correspondingly, this kind of determining an overfilling, however, is not applicable to various filling level measuring devices, such as, for example, radar sensors, since filling product covering the radar antenna leads to a strong reflection of the signal, and therewith to an increase of the amplitude.
A similar arrangement may be seen from German Patent Application DE 195 38 678 A1. Finally, general reference is made to German Patent Application DE 198 17 378 A1 disclosing in general a filling level measuring device, which is less sensitive and easier to service as compared to known float-type switches, for which purpose the level of a material is detected via reflection signals of an electromagnetic radiation, and constitutes here in particular a so-called TDR filling level measuring device.
The present invention relates to a method for detecting an overfilling of a receptacle filled with a filling product. It is in particular supposed to create a possibility that a filling level measuring device working in particular on the pulse echo principle and scanning a reflected echo signal, is allowed to automatically detect an overfilling of a receptacle.
According to a first exemplary embodiment of the present invention, a method for the non-contact determination of an overfilling of a receptacle filled with a filling product is described where an envelope curve is generated from echo signals reflected on a filling product surface, the echo signal amplitude in a predetermined short range of the envelope curve is mathematically processed and compared to a predetermined reference value, and upon overstepping the predetermined reference value, a signal representative of the overfilling of the receptacle is outputted.
According to a further exemplary embodiment of the present invention, an evaluation arrangement is proposed for the non-contact determination of an overfilling of a receptacle filled with a filling product, by evaluation of echo signals of a filling level measuring device, which echoes are reflected on a filling product surface, which filling level measuring device includes a processing arrangement, which mathematically processes the echo signal amplitude in a predetermined short range of an envelope curve generated from echo signals reflected on a filling product surface, and compares same to a predetermined reference value, and outputs a signal representative of the overfilling of the receptacle upon overstepping the predetermined reference value.
According to yet another exemplary embodiment of the present invention, a filling level measuring device is proposed for the non-contact determination of the filling level of a filling product in a receptacle, comprising a transmitting and receiving arrangement for transmitting signals and for receiving echo signals reflected on a filling product surface, and an evaluation arrangement for the non-contact determination of an overfilling of a receptacle filled with a filling product by evaluation of echo signals reflected on the filling product surface. The evaluation arrangement includes a processing unit, which mathematically processes the echo signal amplitude in a predetermined short range of an envelope curve generated from echo signals reflected on the filling product surface, and compares same to a predetermined reference value, and upon overstepping a predetermined reference value, outputs a signal representative of the overfilling of the receptacle.
The present invention utilizes the large signal amplitudes arising in the short range of the echo signal for detecting an overfilling. Thus, from echo signals reflected on a filling product surface, an envelope curve is generated. The echo signal amplitude is mathematically processed in a predetermined short range of the envelope curve, and is compared to a predetermined reference value. Upon overstepping the predetermined reference value, a signal representative of an overfilling of the receptacle is outputted.
In particular, it is advantageous when the echo signal amplitude is integrated in the predetermined short range.
In general, it has to be noted that the xe2x80x9cshort rangexe2x80x9d of an envelope curve is in particular that range, which starts at the signal radiation arrangement, such as, for example, an ultrasonic transducer or a radar antenna, and extends up to 2 m or more from same.
If the transmission signal concerned is a radar pulse of a radar sensor, then it is advantageous to fix the predetermined short range in dependence on the transmission signal frequency. In particular, it is also advantageous to fix the predetermined short range in dependence on the kind of the filling product, i.e. depending on the fact whether the filling product is a liquid or a bulk material. With the evaluation of radar pulses of a radar-filling level measuring device, it is in particular advantageous to fix the predetermined short range in addition also in dependence on the kind of the antenna used for transmitting and receiving the radar pulses. Depending on whether a rod or a horn antenna is concerned, the short range of interest here, has to be fixed differently.
In case the signals to be evaluated are ultrasonic signals, it is advantageous to fix the predetermined short range in dependence on the configuration of the sound transducer for sending and receiving ultrasonic pulses, and in dependence on the transmission frequency.
It is in particular advantageous to fix the short range so that it extends from the beginning of the envelope curve up to that point of the envelope curve where the amplitude value is higher than the system noise by a predetermined safety distance. Thus, for example, the general system noise at a transmission frequency of 24 GHz, may be at approx. 20 dB. If a safety distance of 10 dB is, for example, selected, then the short range extends from the beginning of the envelope curve up to that point where the amplitude value is again 30 dB. In the aforementioned example, the short range to be examined would therewith be approx. 1 m.
The output of a signal representative of an overfilling of the receptacle basically makes only then sense when the safe range for measuring the filling level is left. Accordingly, it is in particular purposeful to compare the distance of a useful echo to a predetermined distance value, and to output a signal representative of an overfilling of the receptacle only for that case that the distance of the useful echo is smaller than the predetermined distance value.
On the other hand, it may in addition, or also as a single interrogation be purposeful to compare the signal-noise distance to a predetermined signal-noise distance, and to output a signal representative of an overfilling of the receptacle only for that case that the signal-noise distance is smaller than a predetermined signal-noise distance. Under the term signal-noise distance, also called measurement safety, the amplitude of the filling level is to be understood, which is above the system noise or the dying-out transmission signal.
It is in particular advantageous, when upon detection of an overfilling of the receptacle, a trouble message is outputted, which is then used by other systems. Alternatively, it is also possible to switch an alarm relay when the detection of an overfilling of the receptacle is ascertained by the aforementioned measures. A further alternative consists in maintaining an initial value preferably upon detection of an overfilling of the receptacle, for as long until the overfilling is no longer present.
An exemplary embodiment according to the present invention of an evaluation arrangement for the non-contact detection of an overfilling of a receptacle filled with a filling product by evaluation of echo signals of a filling level measuring device reflected on a filling product surface, comprises a processing unit, which automatically processes the signal echo amplitude mathematically in a predetermined short range of an envelope curve, and compares same to a predetermined reference value. Upon overstepping the predetermined reference value, the evaluation unit outputs a signal representative of the overfilling of the receptacle.
The evaluation unit may be configured to perform one or more features of the method according to the present invention.
An evaluation unit according to the present invention may be configured to be an autonomous unit spatially-physically separate from the actual filling level measuring device. Thus, it would, for example, be imaginable to integrate such an evaluation unit into a control panel. Depending on the given facts, however, it is also extremely advantageous to directly integrate such an evaluation arrangement into the filling level measuring device. In this case, the evaluation arrangement constitutes a part of the filling level measuring device. Over a conventional communication line, the overfilling signal is then outputted to other means such as, for example a control panel, or, if there is no overfilling condition given, a signal representative of the filling level is outputted.
It has still to be noted here that, of course, any programs, which can serve for realizing one of the above-described methods, fall within the scope of protection of the present invention, and have likewise to be protected as such.